Solid-state disk lasers and the like are being used in many new applications. Examples of such applications may include but are not necessarily limited to military laser target illuminators or designators and commercial laser material processing applications such as cutting, welding, drilling or the like. Such applications typically require laser powers between about 5 kW and about 10 kW. A single solid-state disk laser may be able to generate enough power for an industrial laser device; however, the amplifier disk may be relatively thin, about 0.5 to 2.5 mm, which may translate to a rather short gain length. Consequently, if a single solid-state disk laser amplifier is used in a traditional single pass resonator, such as the single-pass laser resonator 100 illustrated in FIG. 1, the resonator gain would be too low to buildup enough recirculating power to saturate the solid-state gain medium of the disk laser 102. In FIG. 1, the solid-state disk laser (SSDL) 102 may be thermally coupled to a heat sink 104. Pump beams 106 may be directed on the SSDL 102 to generate an amplified beam 108 directed through an output coupler 110. A reflective coating 112 may be disposed between the SSDL 102 and the heat sink 104 on a surface of the SSDL 102.
The U.S. Pat. No. 7,463,667 granted on Dec. 9, 2008 to the Applicant and incorporated herein by reference in its entirety discloses a laser system including a solid-state laser gain material (LGM) and a plurality of relay mirrors for multi-passing a laser beam to and from the LGM. Referring now to FIG. 2, the laser system 200 requires that for each laser beam pass to the LGM disk 206, two relay mirrors are used. It is well known in the art that the surface accuracy of relay mirrors is limited to a fraction of a laser wavelength, typically to about 1/20th a wave at 628 nm wavelength. A wavefront of a laser beam reflected from such a mirror is imparted at least some of the inaccuracy of the mirror surface. As a results, the beam quality (BQ) of the laser beam is significantly degraded with each reflection from a relay mirror. It is therefore desirable to achieve laser amplification with fewer relay mirrors. Furthermore, the configuration of relay mirrors disclosed in the U.S. Pat. No. 7,463,667 limits the laser system to only one LGM, thereby limiting the laser power output.
In summary, prior art does not teach a laser system with LGM disks and multi-pass beam delivery optics capable of producing very high average power with good beam quality which is also very compact and robust. It is against this background that the significant improvements and advancements of the present invention have taken place.